Here are a few snippets of trivia about the ways we measure things.

Watch the opening credits of Mork and Mindy... there is a shot of a sign as they drive into Boulder, Colorado. This sign shows the elevation of the city in both feet AND meters! This is quite an old TV show and demonstrates that metrication was happening in the USA a long time ago.

3.25 inch floppy disks have never been 3.25 inches... get a ruler out and take a look. They are actually 90x94mm and neither of those measurements is 3.25 inches!

Roads are designed and built using the metric system... as are the road signs themselves. Road builders have to convert to imperial in order to correctly locate signs that show distances.

Many things we use have ALWAYS been measured using metric... such as electricity (volts, amps and watts) and paper (A4 is a metric measurement, as is the C range used for envelopes). I don't ever recall 35mm photographic film being described as anything else! The term "calorie" used by many on diets is a metric measurement, although not really used correctly.

Hospitals and doctors use metric... whenever you're measured or weighed. Your measurements will be recorded in metric, however it is not uncommon for medical staff to convert to imperial before telling you what they are. That includes weights of new-born babies!

Standards organisations use the metric system to define imperial measurements... there are international treaties that strictly define the size of the inch, foot and mile using metric units. The same can be said of other weights and measures.

Non-metric units differ... depending on what country you're in. For instance a gallon in the UK is about 4.5 litres but in the USA it's 3.8 litres. A UK pint is 0.56 litres compared to 0.47 in the USA and 1 fl-oz is 28.3ml in the UK and 29.57ml in the USA. If you're going to weigh something you'll find that 1 hundredweight in the UK is 50.8kg but in the USA is 45.36kg; on the same basis 1 ton (defined as 20 hundredweight in both countries) is 1016kg in the UK but is 907.2kg in the USA. 

A mile is not always a mile... A mile on land (a "Statute Mile") is 1609.344 metres but a mile on sea or air (a "Nautical Mile") is 1853.184. Beware though as you also have a "Sea Mile" which is the distance travelled across 1 minute of latitude on a map and if you buy a US Survey map the mile is 1609.347 metres (3 mm longer than a standard mile... not much but it adds up!)

Some metric units are named after Brits... Faraday, Gray, Joule, Newton, Watt and Kelvin are all names of metric units named after British scientists. 

Imperial measures are not British... The Mile for instance was a Roman measurement - usually defined as 1000 paces taken by a trained soldier (yes, 1000!). Fahrenheit was a German - and his temperature scale was invented only 40 years before the Celcius scale!

The USA have two different definitions of the "foot"... the US equivalent of the Ordnance Survey, the US Geodetic Survey, produce maps which are measured in what is known as the "Survey Foot". This differs by a very small amount from the standard (or International) foot. The reason for this? When the USA adopted the international standard foot as being 0.3048 metres they decided that instead of re-drawing or re-measuring their maps in metric as was done in the UK that they would retain the "old" foot which is defined as 1200/3737 metres, which makes 1 survey foot = 1.000002 international foot. Just be careful if you use one of these maps... over 1km thats about 6 metres difference, just imagine that over hundreds of km's!

The moon is metric... in early 2007 NASA made the announcement that for all their work relating to the moon that everything would be in metric. The reason? to make things easier for everybody. One example they gave was something like this: the Russians have a vehicle that has broken down and the nearest engineer is an American astronaut. When he shows up to lend a hand it helps everybody if he has the right tools! What this does mean is that all US based contractors who want to sell anything to NASA for use on the moon will also have to use metric. 

The only things in everyday life in the UK which aren't allowed to be metric... are draught beer sold in pubs in returnable containers, milk delivered to the doorstep in returnable bottles and most measurements on our roads. This combination has been referred to as "drinking and driving". In comparison all drugs, illegal or otherwise, are sold in metric in the USA.